fix(ci): compare release changelog against previous streamkit tag only

[staging-devin-ai-integration]

Summary

Fixes the release changelog to compare against the previous streamkit release tag instead of any tag (including plugin tags). The git describe command in the changelog generation step now uses --match 'v[0-9]*' to only consider streamkit version tags (e.g., v0.2.0) and skip plugin tags (e.g., plugin-helsinki-v0.1.0).

Root cause: git describe --tags --abbrev=0 HEAD^ finds the nearest reachable tag of any kind. Since plugin tags like plugin-helsinki-v0.1.0 were closer to v0.3.0-dev than v0.2.0, the changelog was generated against the wrong base — as seen on the v0.3.0-dev release page.

Review & Testing Checklist for Human

• Verify the glob pattern v[0-9]* correctly matches all current and expected future streamkit version tags (e.g., v0.2.0, v0.3.0-dev, v1.0.0-rc1) while excluding all plugin tags (plugin-*-v*)
• This change cannot be validated by CI — consider manually verifying with git describe --tags --abbrev=0 --match 'v[0-9]*' <commit>^ at a commit where plugin tags sit between two streamkit release tags

Notes

• Requested by: @streamer45
• Link to Devin run

[staging-devin-ai-integration]

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